1. Field of the Invention
The present invention relates to an infrared-rays detector for detecting infrared energy radiated from a human body in order to detect the existence or movement of a human body.
2. Description of the Prior Art
A pyroelectric element is used widely to detect infrared-rays radiated from a human body. The pyroelectric element set for each of monitor areas outputs a current in correspondence to infrared radiation. Then, in an infrared-rays detector, a current-to-voltage converter converts the current to a voltage, and a voltage amplifier amplifies the voltage. When the output voltage exceeds a predetermined level, it is decided that a human body is detected, and a detection signal which means that a human body exists or moves in the monitor area is outputted.
The infrared-rays detector is designed to have the frequency characteristic for movement of a human body, and it has a characteristic of band-pass filter having a center of transmission band at about 1 Hz. Then, the sensitivity to a human body is enhanced, and a malfunction is prevented to be caused by signals at frequencies irrelevant to movement of a human body.
However, the pyroelectric element outputs a one-shot noise called as popcorn noise disadvantageously. It is thought that the popcorn noise is ascribed to generation of unnecessary electric charges in the pyroelectric element, and the unnecessary electric charges are generated by compression or tensile stress centered at defects in materials of a pyroelectric plate or electrodes or at pitchings, microcracks or the like generated by dicing or the like, due to differences in thermal expansion coefficient in a pyroelectric plate, electrodes, a support, an adhesive agent, a circuit board or the like in the pyroelectric element.
Previously, in order to reduce the occurrence of the popcorn noise as one-shot output noise, it is proposed to optimize the materials for the support, the circuit board, the electrically conductive adhesive, or the like, or to change the structure of the pyroelectric element. However, even if such proposals are adopted, the occurrence of the popcorn noise cannot be suppressed completely in the infrared-rays detector, and a malfunction is liable to be caused by the popcorn noise.